JAJSJR5A October 2019 – November 2020 LMR50410-Q1
PRODUCTION DATA
The following operating description of the LMR50410-Q1 refers to Section 8.2 and to the waveforms in Figure 8-1. The LMR50410-Q1 is a step-down synchronous buck converter with integrated high-side (HS) and low-side (LS) switches (synchronous rectifier). The LMR50410-Q1 supplies a regulated output voltage by turning on the high-side and low-side NMOS switches with controlled duty cycle. During high-side switch ON time, the SW pin voltage swings up to approximately VIN, and the inductor current, iL, increases with linear slope (VIN – VOUT) / L. When the high-side switch is turned off by the control logic, the low-side switch is turned on after an anti-shoot-through dead time. Inductor current discharges through the low-side switch with a slope of –VOUT / L. The control parameter of a buck converter is defined as Duty Cycle D = tON / TSW, where tON is the high-side switch ON time and TSW is the switching period. The converter control loop maintains a constant output voltage by adjusting the duty cycle D. In an ideal buck converter, where losses are ignored, D is proportional to the output voltage and inversely proportional to the input voltage: D = VOUT / VIN.
The LMR50410-Q1 employs fixed-frequency peak-current mode control. A voltage feedback loop is used to get accurate DC voltage regulation by adjusting the peak-current command based on voltage offset. The peak inductor current is sensed from the high-side switch and compared to the peak current threshold to control the ON time of the high-side switch. The voltage feedback loop is internally-compensated, which allows for fewer external components, making designing easy, and providing stable operation when using a variety of output capacitors. The converter operates with fixed switching frequency at normal load conditions. During light-load condition, the LMR50410-Q1 operates in PFM mode to maintain high efficiency (PFM version) or in FPWM mode for low output voltage ripple, tight output voltage regulation, and constant switching frequency (FPWM version).